That's right. No interaction between the two is mentioned in the novel explicitly. But if Rocco built a secret regime without Tom's knowledge, there had to be interaction between Michael and Rocco. Vitos says "I told Michael that Lampone’s secret regime would not escape your eye." This looks like it was Michael's idea. And most probably he contacted him directly, without the interference of Clemenza or Tessio. Who else could have been a middle man?